We are developing model systems in laboratory rats to improve our understanding of the neoplastic potential of early abnormal proliferations in urothelium. We have found that mechanical trauma to the bladder may in a few weeks produce calculi, papillomatosis, and hyperplasia (Cancer Research, 35: 3786,1975). In the coming year we will expand our experience with proliferations produced by trauma, and compare these abnormalities with early lesions produced by chemical carcinogens in the rat bladder. Comparisons will be made using two approaches, transplantation and tissue culture. For evaluation by transplantation, we will use the heterotopic urinary bladder model (Cancer Research, 34: 2773,1974). For evaluation in vitro we will compare these histologically similar lesions with the same methods we are using and developing in our study of low grade clinical bladder cancer. BIBLIOGRAPHIC REFERENCES: Toyoshima, K. and Leighton, J.: Bladder Calculi and Urothelial Hyperplasia with Papillomatosis in the Rat Folliwing Insertion of Chalk Powder in the Bladder Cavity and Subsequent Trauma of the Bladder Wall. Cancer Res. 35: 3786-379l,1975.